With the advent of the recent wireless multimedia era, the necessity to transmit a large capacity of data at a high speed over radio channels increases rapidly. Large transmission output and transmission bandwidth compared to general data transmission are required for high-speed data transmission. Thus, there is needed a method for reducing an interference signal and efficiently transmitting a desired signal to perform high-speed communication. One of alternatives for reducing an interference signal and guaranteeing a high reception power is a smart antenna technology, that is, a beamforming technology.
According to conventional beamforming, a Base Station (BS) divides a cell into a predetermined number of sectors and performs beamforming in each of the sectors separately. Thus, the BS has to include antennas on a per-sector basis by the number necessary for beamforming. For instance, if 4 antennas are used for beamforming, the BS has an antenna construction of FIG. 1. In FIG. 1, the whole of 12 antennas of the BS are classified into alpha (α) sector antennas, beta (β) sector antennas, and gamma (γ) sector antennas and used for beamforming for each sector. If beamforming is, for example, performed for an arbitrary mobile station (MS) located in an alpha (α) sector, a beam coefficient used is expressed in Equation 1 below:W60 =(Hdα)H   (1)Here,Hdα=[hdαant 1 . . . hdαant N]where Wα is the beam coefficient for sector α, and hdαant N is the channel for antenna N in sector α.
As noted in Equation 1, the base station (BS) considers only the channel in the alpha sector when performing the beamforming for the MS located in the alpha sector. Thus, upon beamforming, the BS does not control interference toward a neighbor sector and therefore, has to reduce a magnitude of a beamforming signal directing to a sector boundary. That is, the beamforming is divided and performed on a per-sector basis respectively and therefore, there is a drawback that as shown in FIG. 1, a magnitude of a beamformed signal directing to a sector boundary is reduced compared to a magnitude of a beamformed signal directing to a sector center. Because of this, an MS located at the sector boundary obtains a low beamforming gain. Also, there is a drawback that the BS gets complex more in construction because the BS has a plurality of antennas on a per-sector basis.